TechEdSat-4 is a 3U CubeSat mission developed , integrated by, and tested at NASA Ames (PI: Marcus S. Murbach) in partnership with student interns from SJSU (San Jose State University) in California and the University of Idaho. TechEdSat-4 is funded by NASA Ames and the Human Exploration and Operations Mission Directorate at NASA Headquarters. The objective of the TechEdSat-4 mission is to demonstrate two new technologies including a system to provide satellite-to-satellite communications and information about the spacecraft's health, as well as an upgraded exo-brake device to demonstrate a passive deorbiting system capable of accurately reentering Earth's atmosphere. 1)

The satellite builds on the success and lessons learned from previous TechEdSat projects, particularly TechEdSat-3p, a 3U CubeSat that was deployed on J-SSOD (JEM-Small Satellite Orbital Deployer) from the ISS on Nov. 20, 2013 and became the first mission to perform an in-flight test of an exo-brake passive deorbit system.

TechEdSat-4 is the fourth generation in the continuing TechEdSat Series. The TechEdSat-4 (TES-4) builds upon the success of TES-1, -2, and -3 by continuing to demonstrate increasing capability for CubeSats in the areas of communications and satellite reentry. The TES project uniquely pairs advanced university students with NASA Ames researchers in a rapid design-to-flight experience over the course of 1to2 semesters. The TES Series not only provides a rapid platform for testing technologies for future NASA Earth and planetary missions, but also provides students early exposure to flight hardware development and management. 2)

TechEdSat-4 has a size of 10 cm x 10 cm x 34 cm and a mass of 2.68 kg. It uses COTS (Commercial Off-The-Shelf) components and largely reuses heritage components that flew on the TechEdSat-1 and TechEdSat-3p missions (launch Aug. 3, 2013). TechEdSat-1 (launched on July 21, 2012) was a 1U CubeSat designed to test the basic satellite design, avionics, stabilization and communication systems. This 1U CubeSat bus is essentially reused on TechEdSat-4 to provide the basic satellite functions such as commanding, power generation & supply as well as communications while the other 2 units of the satellite (2/3 of its volume) carry the payload. 4)

EPS (Electrical Power Subsystem): The TechEdSat EPS features a scalable plug-and-play architecture that allows the addition of batteries and solar panels transitioning from a 1U to a 3U spacecraft. The satellite features body-mounted solar panels, dedicated electronics for power distribution and the management of the state of charge of a Li-ion battery. Latch-up current limiters are used for circuit protection.

Spacecraft control is provided by a ÅAC Microtec microprocessor that controls all satellite functions including attitude control and communications, that are accomplished via Iridium and GPS satellites, using a short-burst data modem. TechEdSat-4 is also demonstrating a satellite-to-satellite communications system that will allow for more frequent communication sessions with the satellite that lead to a higher accuracy of satellite altitude and position predictions which are important for the operation of the exo-brake.

Launch: The TechEdSat nanosatellite was launched as a secondary cargo payload on July 13, 2014 on the Cygnus CRS Orb-2 ISS resupply mission. The launch vehicle was Antares-120 of OSC and the launch site was MARS (Mid-Atlantic Regional Spaceport), Wallops Island, VA. The pressurized Cygnus spacecraft delivered 1,657 kg of cargo to ISS, including 300 kg of standard crew supplies, systems hardware and of science and research equipment. 5)

• Planet Labs' Flock-1b: A flock of 28 nanosatellites (additional to 28 Flock-1 nanosatellites launched on January 9, 2014) from Planet Labs of San Francisco are aboard to take pictures of Earth. After deployment from the Japanese JEM module (using the NanoRacks LLC Smallsat Deployment Program). Once deployed, these two flocks will work in unison and capture imagery of the entire planet on a more frequent basis, forming the largest constellation of imaging satellites in Earth orbit. 7)8)

• TechEdSat-4 is a small CubeSat, built by NASA/ARC (Ames Research Center) in California that will investigate technology to return small samples to Earth from the space station. TechEdSat-4 will deploy using the NanoRacks services. Its primary objectives are to further develop a tension-based drag device, called exo-brake, and demonstrate frequent uplink/downlink control capabilities.

• GEARSSAT (Globalstar Experiment And Risk Reduction Satellite) , a CubeSat with a Globalstar communications terminal,built by NearSpace Launch. The objective is to study the Globalstar communications constellation.

• LambdaSat, a 1U Cubesat developed and operated by the Lambda Team, an international group including Greek scientists and students from San Jose, USA. The objective is to measure radiation effects on graphene material in LEO, and tracking vessels with an AIS receiver inside its footprint around the globe.

• Fifteen student experiments of the "Charlie Brown" mission are aboard and hosted by the SSEP (Student Spaceflight Experiment Program), an initiative of NCESSE (National Center for Earth and Space Science Education) and NanoRacks. They will investigate plant, lettuce, raddish and mold growth and seed germination in zero-G, penecilium growth, corrosion inhibitors, oxidation in space and microencapsulation experiments.

The NanoRacks CubeSats/nanosatellites are delivered to the ISS already integrated within a NRCSD (NanoRacks CubeSat Deployer). The NRCSDs can be stored inside the ISS until a deployment is requested. 9)

The secondary payloads (Flock-1b, TechEdSat-4, MicroMAS-1, GEARSSAAT, and LambdaSat) will be deployed from the Space Station using a deployment mechanism supplied by NanoRacks LLC. The System uses the MPEP (Multi-Purpose Experiment Platform) of the JEM (Japanese Experiment Module) to which the NRCSDs (NanoRacks CubeSat Deployers) are attached. The dispenser holds up to sixteen 3U CubeSats and is attached to the MPEP that can be grappled by the JRMS (JEM Remote Manipulator System) and deploy the satellites in pairs upon command issued from inside the ISS or the JAXA Control Center in Tsukuba, Japan.

For a deployment, the platform is moved outside via the Kibo Module's Airlock and slide table that allows the JRMS arm to move the deployers to the correct orientation for the satellite release and also provides command and control to the deployers. Each NanoRacks CubeSat Deployer is capable of holding six CubeSat Units - allowing it to launch two 3U satellites or a number of 2U and 1U satellites.

Deploying CubeSats from ISS has a number of benefits. Launching the vehicles aboard the logistics carrier of ISS visiting vehicle's reduces the vibration and loads they have to encounter during launch. In addition, they can be packed in protective materials so that the probability of CubeSat damage during launch is reduced significantly. Also, once arriving at the Space Station, the satellites can be checked pre-deployment, making sure any damage is detected before committing them to flight.

Mission status:

• Aug. 2016: The TechEdSat-4 (TES-4) exo-brake deployed, changed the drag on the CubeSat, resulting in early orbital reentry. The time frame for deorbit and the quantitative drag assessment from this experiment is very useful for designing future SPQR (Small Payload Quick Return) methods and spacecraft. TechEdSat-4 experienced a 4 week deorbit in 2015. 10)

- The future TES-5/PS5 features improved GPS tracking and a modulated exo-brake allowing more precise control of the exo-atmospheric drag and therefore the reentry time and location. The TES-5/PS5 is a significant upgrade from TES-4, featuring an improved C&DH built around the Intel Edison mobile computing platform, the core of new PhoneSat. This CubeSat has an ISM-band WiFi downlink for data, significantly reducing the cost of such communication services. It features multiple cameras to help verify exo-brake deployment and modulation. The GPS tracking should give precise orbital trajectories leading to much better drag assessment, reentry targeting and other benefits.

Figure 3: TES-3/TES-4 flight test data Image credit: NASA/ARC)

• After an ISS onboard waiting period of 8 months (Table 1), the TechEdSat-4 nanosatellite was deployed on March 3, 2015. NASA mission controllers confirmed that a small satellite has successfully entered its orbit, setting the stage to test technology that could enable rapid return of payloads from space. Over the next four weeks, the TechEdSat-4 satellite will deploy a second-generation exo-brake, an aerodynamic drag device, to perform a maneuver that will cause the satellite to de-orbit and reenter Earth's atmosphere. 11)

- About 30 minutes after the Nanoracks CubeSat Deployer jettisoned it from the space station, the autonomous free-flying satellite powered on. The spacecraft received a command via email and deployed its specially-designed parachute-like exo-brake, which operates as a passive drag device at the extremely low pressures found at the top of the atmosphere. Engineers also confirmed the satellite has demonstrated new satellite-to-satellite communications technologies to provide precise information about the spacecraft's health and position.

- TechEdSat-4 is equipped with a short-burst data satellite modem combined with a GPS receiver to perform communications functions, including providing data about the spacecraft's health, space environment and location. Together, these technologies replace ground stations used for tracking, rapid data retrieval and uplink capability, and permit satellite control via secure email.

NanoRacks LLC of Houston, TX, is the only commercial company of NASA, providing on-board and on-ground services to the general 'small payload' research community of the International Space Station (ISS).

The NanoRacks deployment services for small satellites started initially by using the J-SSOD (JEM-Small Satellite Orbital Deployer) of JAXA. In October 2012, NanoRacks became the first company to coordinate the deployment of small satellites (CubeSats/nanosatellites) from the ISS via the airlock in the Japanese Kibo module. This deployment was done by NanoRacks using J-SSOD.

In 2013, NanoRacks sought permission from NASA to complement the JAXA J-SSOD with a larger model, NRCSD (NanoRacks CubeSat Deployer), provided by NanoRacks to hold larger and more satellites. This new NanoRacks deployer system, was designed, manufactured and acceptance-tested by NanoRacks and launched on the Orbital Sciences Cygnus CRS-1 flight on January 9, 2014. It permitted NanoRacks the subsequent release of 33 CubeSats of their customers, using the new NanoRacks deployer system with the JEMRMS (JEM-Remote Manipulating System) of JAXA – to grapple and position for deployment.

The NRCSD deployer system broke down in August 2014, failing to release satellites when commanded. During the troubleshooting process in September, two satellites were inadvertently released. The deployers were returned inside the ISS through the airlock in the Japanese Kibo module in mid-September.

NanoRacks had built new deployers to correct the problem, it worked with NASA and other ISS partners to also attempt to repair the deployers currently on the station. After several months of hard work, the NanoRacks team was able to make adjustments to the deployers. The problems with the deployers were traced to screws that were not tightened correctly as well as issues with a power feed.

The repair work included installation of a new electronics system for the deployer and latches to prevent the premature deployment of the satellites. A SpaceX Dragon cargo spacecraft delivered the repair hardware to the ISS in January 2015. The station's crew made the repairs and successfully tested the latches on Feb. 17, and planned to attempt satellite deployments in the week of Feb. 23, 2015.

Table 1: Some background of the NRCSD breakdown and renewed system provision which caused considerable deployment delays for several customers. 12)

• On July 16, 2014, Cygnus CRS Orb-2 arrived at the ISS and was captured by Commander Steve Swanson as he maneuvered Canadarm2 from a robotics workstation inside the station's seven windowed domed Cupola. In the following days, the station crew will unload the cargo from the docked spacecraft. The first CubeSat deployment via the NanoRacks deployer is now scheduled for the end of July. It should take about a week to deploy the first block of CubeSats. 13)
Cygnus will remain attached to the station approximately 30 days until August 15, 2014. 14)

Experiment complement: (Exo-Brake, Intersatellite Communication)

Exo-Brake:

The exo-brake is deployed once the satellite is released to demonstrate a passive deorbit system for satellites. The assembly is a simple drag-based deorbit mechanism, like a specially designed parachute that operates at extremely low pressures, which will eventually enable small samples to be returned from the space station or other orbital platforms. Exo-brake is a tension based structure that has a number of advantages over other designs such as a high stability and the possibility of drag modulating to provide a targeting capability.

The initial exo-brake version was successfully flown on the TechEdSat-3 nanosatellite in late 2013. The evolving instrument set of TechEdSat-4 includes an onboard GPS receiver, as well as a novel command uplink/downlink capability. The principal objectives are to further develop the tension-based drag device (exo-brake) and demonstrate a frequent uplink/downlink control capability. 15)

The next steps will include a drag- modulation scheme which will lead to improved targeting at the von Karman altitude. Future applications include a sample return capability – as well as a novel means of testing future small scale reentry concepts for planetary mission applications. 16)

Figure 4: Artist's rendition of the TechEdSat-4 NanoRacks deployment from the ISS and subsequent release of the exo-brake (image credit: NASA)

Intersatellite Communication

The objective of the evolving TechEdSat-4 experiment is to demonstrate the use of an Iridium modem combined with a GPS receiver as well as a novel command uplink/downlink capability to communicate accurate positional and deorbit information.

Eventually, these will be combined to provide a controlled sample return capability from the ISS or other orbiting platforms.

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).